High performance collet for electrical connectors



June 25, 1968 I J. A. NAVA 3,390,376

HIGH PERFORMANCE COLLET FOR ELECTRICAL CONNECTORS F 7; INVENTOR.

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BY ,qw w, ATTORNEYS June 25, 1968 J, A. NAVA 3,390,376

HIGH PERFORMANCE COLLET FOR ELECTRICAL CONNECTORS Filed March 5, 1967 4Sheets-Sheet 2 Fi-Z ff 47 46a 54 55 44 46 INVENTOR.

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BY ATTORNEYS J. A. NAVA June 25, 1968 HIGH PERFORMANCE COLLET FORELECTRICAL CONNECTORS Filed March 5. 1967 4 Sheets-Sheet 4 Y w 5 M u mlb w /ddc INVENTOR. Jaaa/w 4. Alm/4 By rw-h; nrt/rw ATTORNEYS UnitedStates Patent 0 3,390,376 HIGH PERFDRMANCE COLLET FOR ELECTRICALCGNNECTORS Joseph A. Nava, Villa Park, Ill., assignor to ThePylelglational Company, Chicago, Ill., a corporation of New ersey FiledMar. 3, 1967, Ser. No. 620,408 11 Claims. (Cl. 339-217) ABSTRACT OF THEDISCLGSURE An electrical connector comprisingan insulator block,registered :bores extending through the block and collets mounted Withinthe bores for receiving electrical contacts and for securely holding andpositioning the contacts within the bores. Each of the collets isgenerally tubularly shaped and comprises a circumferentially continuouscylindrical sleeve and a plurality of flexible and resilient fingersprojecting axially from one end of the sleeve. The collet is formed by amachining operation rather than a stamping or punching operation inorder to provide special radial and axial cross-sectionalconfigurations, particularly with respect to the fingers.

Background of the invention The general field of art to which thepresent invention pertains is that of rmulti-pin electric-al connectorsand a more specific field of ar-t is that of collets or contactmountings for securing the pins or electrical contacts of `an electricalconnector within the contact-receiving bores thereof.

Multi-pin or multi-contact electrical connectors are widely used innumerous applications. They comprise in most instances a pair ofinsulator blocks through which are formed `a number of axiallyregistered pairs of bores An electrical contact or terminal is carriedin each bore. Each pair of axially registered bores houses a pair ofmating contacts which come together in electric circuitmaking relationupon assembly of the insulator blocks.

One electrical contact or terminal widely used is known as the pin type,and each pair of such contacts comprises a male member which ispartially inserted into the bore of a mating female member. Generally,all of the male members are carried in one insulator block and all ofthe female members in the other block. This rule is not rigorouslyfollowed, however, and furthermore there are electric terminals otherthan the pin type used in the electrical conncctor art. It is notuncommon for a single electrical connector to employ as many as 30 ormore pairs of electrical contacts. The contacts are generally insertedfrom the back sides of their respective insulator blocks, the oppositeor front sides :being identified as those facing the other insulatorblock in the assembled connector. The individual contacts are connectedto suitable conductors such as wires at the back sides of the blocks.

The male members usually protrude out of the bores of their insulatorblock, whereas the female members usually reside entirely within thebores of their block. By the simple expediency of bringing the twoinsulator lblocks together into abutting or assembled relation amultitude of electric circuits corresponding to the number of pairs ofmale and female contacts can be simultaneously completed. When the twoblocks are separated all of the circuits are broken.

Means are provided for mounting the male and female contacts within thebores of their respective insulator blocks. Such mounting means shouldpreferably be capable of withstanding the substantial forces that may beapplied to the contacts in the Iassembly and disassembly of lCC theconnector many times without failure -or breakage thereof.

The contact mounting means generally comprises a plurality of colletsinserted respectively into the bores of the insulated blocks. In orderto prevent the contacts from being pushed toward the back sides of theinsulator blocks during assembly of the connec-tor, i.e., when the malemembers yare inserted into tne female members, tne collets are eachprovided with a plurality of radially inwardly extending tines orfingers having shoulders, edges or other stop surfaces for abuttinglyeng-aging complemental surfaces formed on the contact members. Colletsare generally used for this service -because yof the ease with which thecontacts can -be removed for serv-ice, replacement or the like. Merelyby inserting a tubular contact removal tool around the contacts and intothe bores from the front sides of the insulator blocks, the tines can bespread radially outwardly in the bores and the contacts can then beeasily removed from the bores.

In many applications of electrical connectors of the type describedhereinabove the individual male and female contact members are quitesmall and the size of each of the contact-mounting collets isparticularly diminutive. oftentimes the collets are about inch in lengthand j/16 inch or smaller in diameter. The tines or fingers which areformed on the collets to engage and restrict axial movement ofthecontacts may be extremely small.

As a result, the collet tines or fingers of collets heretofore known inthe electrical connector art can undergo a relatively small number ofassembly cycles. Each time the two insulator blocks of la connector arere-assembled, and -the male contacts are pushed into the femalecontacts, substantial forces are imposed on each of the little tines ofthe collets in preventing the male and female contacts from movingtoward the back side of their respective insulator blocks.

Prior art connectors of which I am aware have a contact removalcapability of about 50 to 60 times. In other words, the contacts can bedisassembled from the insulator blocks by opening the collets, with anappropriate tool, and re-assembled after servicing the contacts, a totalof 50 to 60 times. This low contact removal capability is generally dueto the inability of the small tines of the collets to withstand thefatigue stresses resulting fro-m repeated fiexure.

The tines may fail in several different ways. First of all, due to theforces imposed thereon they may take a permanent deformed set, thusprecluding snug engagement with the shoulders of the contacts. Inaddition the tines may fracture due to fatigue or overstress. Because ofthis low contact removal capability of the collets, applications ofelectrical connectors are generally restricted to those which requireinfrequent disassembly and assembly. As a matter of fact, as a result ofcollet failure many government and industry specifications require acontact removal capability of only ten times. To greatly increase thecontact removal capabilities of electrical connectors withoutdiminishing any of the advantages which attend the use of collets is aprincipal object of the present invention.

Summary of the invention Briefly, the present invention relates to anelectrical connector comprising an insulator block having collet andcontact receiving bores extending therethrough. The collets, rather thanbeing made of flat sheet-form material, are machined to a specialconfiguration.

Each of the collets comprises a cylindrical sleeve and a plurality ofcircumferentially spaced contact-engaging fingers (or tines) projectingaxially from one e'nd of the sleeve to jointly surround a contact whenthe contact is inserted into the collet.

Each. of the iingers comprises a major portion adjacent the sleeve, aradially inwardly inclined beam portion extending from the major portionand a head portion at the distal end of the beam portion.

The head portion of each of the lingers comprises a contact engagingsurface formed on the radially inner side thereof to provide, incombination with the contact engaging surfaces of the other headportion, a circumferentially surrounding holding surface for thecontact,

The fingers are also flexible from the points at which they join thesleeve and throughout the beam length from such joints to the contactengaging surface at the head portion, whereby the contact engagingsurfaces formed on the head portions are radially movable or spreadablefrom a free state diameter, which is less than the diameter of theengaging surfaces of the contacts, to an assembled state diameter whichis equal to the diameter of the engaging surfaces of the contact. Thefingers, in addition, are capable of further iiexure, whereby the headportions are radially movable or spreadable, with an appropriate tool,from the assembled state diameter to a diameter suiiiciently larger thanthe contact engaging surface diameter so as to release the Contact andallow its removal from the collet.

Cooperating means are formed on the collets and the walls of the boresfor snap-locking the collets within the bores. In addition the colletsinclude a radial cross-sec tional thickness at the beam portions of thefingers which is less than that at the head portions of the fingers. Thediameter of the inner peripheral wall of each of the fingers is less atthe head portion than at the major portion. The `beam portion of each ofthe fingers extends radially inwardly at an angle to the axis of thecollet which lies within a predetermined range both when the headportion of the finger is at its free state diameter as well as at itsassembled state diameter. Other features include fillets at thejunctions of the beam and major portions and the beam and head portionsof each of the fingers.

Electrical connectors equipped with collets constructed in accordancewith the principles of the present invention and incorporating featuresdescribed hereinabove and hereinafter have been carefully tested interms of the number of times which the contacts can be disassembled andassembled without collet failure. Connectors so constructed have removalcapabilities in excess of 5,000 times, or more than 80 to 100` times thecontact removal capabilities of the connectors of the prior art.

In view of the foregoing it is an object of the present invention toprovide a multi-contact electrical connector having unusually highcontact removal capabilities, for example, in the order of 5,600 timesor more.

Another object of the invention is to provide such an improvedelectrical connector without eliminating or diminishing the advantageswhich attend the use of collettype contact mountings.

Another object is to provide a collet having high durability and highfatigue resistance characteristics.

Another object of the invention is to provide a collet capable ofwithstanding many times more contact removals than those of the priorart without substantially increasing the size of the collet.

Another object of the invention is to provide a collet wherein thestress distributions throughout the tines or fingers thereof isreasonably smooth, with stress concentrations limited to about 1.2 timesthe normal stress and wherein a good correlation exists between thestresses and bending moments of the fingers to provide optimum iiexurecharacteristics and high fatigue resistance.

Still another object of the invention is to provide a collet havingfingers constructed so as to hold a contact more securely and resistbuckling or skew when subjected to an axial load imposed by the contact.

Many other features, advantages and additional objects ot' the presentinvention will become manifest to those versed in the art upon makingreference to the detailed description which follows and the accompanyingsheets of drawings, in which preferred structural embodimentsincorporating the principles of the present invention are shown by wayof illustrative example only.

Brief description of the drawings FIGURE 1 is a fragmentarycross-sectional view of an insulator block of an electrical connectorconstructed in accordance with the principles of the present inventionand having a machined collet of this invention mounting a maleelectrical contact in a bore extending through the block.

FGURE 2 is a side elevational view of the collet shown in FIGURE 1.

FIGURES 3 and 4 are respectively left and right end views ofthe colletshown n FIGURE 2.

FIGURES 5-7 are substantially force vector diagrams useful in explainingthe forces imposed on the fingers of a collet constructed in accordancewith this invention.

FiGURE 8 comprises an enlarged fragmental vertical sectional view of thecollet shown in FIGURES 1-4 and a graph showing the stress and bendingmoment along the active portion of one linger of the collet.

FIGURE 9 is similar to FIGURE 1 but illustrates another embodiment of acollet constructed in accordance with this invention, half of whichcollet is shown in section and the other half of which is shown inelevation.

FIGURES l0 and 11 are respectively left and right elevational end viewsof the collet shown in FIGURE 5.

Description 0]" the preferred embodiments Referring to FIGURE l aninsulator block of a multicontact electrical connector is indicatedgenerally at reference numeral 10. The block 10 has formed therein aplurality of bores which extend from a front side or wall 11 of theblock 10 to a back side or rear wall 12, one of said bores beingindicated at 13.

Bore 13 is formed by a bore wall 14 having an annular ridge 16 formedintegrally therewith and projecting radially inwardly therefrom. Theridge 16 comprises a cylindrical side wall 17 and a pair of axiallyspaced radial end walls 18 and 19.

Extending through the bore 13 is an electrical contact 20. Although theprinciples of this invention are applicable to any type of contact orterminal, the contact illustrated in the drawings is of the pin type,and more particularly a male pin electrical contact. In most connectorassemblies all of the contacts in one insulator block are male contacts.A companion insulator block carries a corresponding number of femalecontacts in axially aligned relation to the male contacts such that whenthe two insulator blocks are brought together all of the male contactsof the one block (for example, block 10) engage the female contacts ofthe companion block in mating relation, as will be understood by thoseskilled in the art.

The contact 20 comprises a cylindrical shank 21 and an enlarged-diametercontact head 22 at one end of the shank adjacent the front Wall 11 ofthe block 10. A concentric reduced-diameter stud 23 projects forwardlyfrom a front wall 24 of the contact head 22 and is received in acomplementary sized bore of a female Contact member of the companioninsulator block in the assembled condition of the connector.

The contact 20 is retained in the bore 13 by means of a contact mountingmember or collet 26. The outer diameter of the contacts 20 is less thanthe diameter of the bore 13, and the collet 26 serves not only to centeror concentrically align the contact 20 within the bore 13, but also torestrict axial movement of the contact backwardly toward the rear wall12 of the block 10 after the contact has been inserted into the collet26. The contact 20 may be prevented from moving forwardly or toward thefront wall 11 of the block 1t) by a conductor terminal attached to theshank 21 which overlies the block rear wall l2, as will be understood bythose skilled in the art.

The collet 26 is generally tubularly shaped and comprises an annular orcylindrical circumferentially continuous sleeve 27 at one end thereofadjacent the block rear wall 12. The sleeve 27 comprises an outerperipheral wall 28 and an inner peripheral wall 29 and a pair of radialend walls 30 and 31. Formed integrally with and projecting axiallyforwardly from the end wall 30 are a plurality of circumferentiallyspaced fingers indicated respectively at reference numerals 32, 33, 34and 35.

Since the fingers 32-35 are identical to one another only finger 32 willbe described in detail and all of the reference numerals applicablethereto are equally applicable to the fingers 33-35.

In radial cross-section finger 32 is substantially segmentallycylindrically shaped along its entire axial length. As shown in FIGURES1-4, finger 32 comprises an outer peripheral wall indicated generally at36 and an inner peripheral wall indicated generally at 37. The diametersand shapes of' portions of the walls 36 and 37 along the axial length offinger 32 differ from one another and will be described in detailhereinafter.

The finger 32 may be conveniently described as comprising threestructurally and functionally different portions along its axial length,a major portion 38, a beam portion 39 and a head portion 40. The majorportion 38 is formed integrally with the sleeve 27. The beam portion 39is axially forward of the major portion 38, that is, toward the frontwall 11 of the insulator block 10. The head portion 40 is axiallyforward of the beam portion 39 adjacent a distal end 41 of the finger32.

An important function of the major portion 38 is to retain collet 26within the bore 13. An important function of the head portion 40 is toengage and to concentrically stabilize the contact 20 within the boreand to restrict axial movement of the contact rearwardly within thebore. Important functions of the beam portion 39 are to connect the headportion 40 to the major portion 38 in a manner so as to provide aradially inward bias to the head portion 40, to resist buckling as thecontact head 22 imposes a load on the head portion 40 and to resistfatigue and other failure modes which could result from metal workinguneven stress distributions and excessive bending.

Finger 32 (as well as fingers 33-35) is resiliently fiexible so that thehead portion 40 is radially movable. Before the contact 20 is insertedinto the collet 26 the fingers assume free state positions asillustrated in the dashed lines at 32 in FIGURE l. After the contact 20is inserted into the collet 26 the fingers are urged radially outwardlyto assembled state positions thereof as shown in the solid lines ofFIGURE 1.

The major portion 38 of the finger 32 comprises spaced parallel outerand inner peripheral walls 42 and 43 and beam portion 39 comprisesfunctionally spaced outer and inner peripheral walls 44 and 45. The headportion 40 comprises an outer peripheral wall 47 and a stepped innerperipheral wall which includes a pair of radially spaced panallelportions 48a and 48h and an inclined portion 48C. A radial wall 49forming a shoulder surface interconnects wall portions 48a an-d 48h.

A fillet 46 is formed integrally with and interconnects the major andbeam portions 38 and 39 and another fillet 46a is formed integrally withand interconnects the beam and head portions 39 and 40. The fillet 46comprises a radial end wall 55 facing the end wall 30 of the sleeve 27,and the complementarily shaped ridge 16 formed on the bore wall 14 isreceived in the recess bounded by walls 55, 30 and 42. i

To mount the contact 20 within the collet 26 the head end 22 of thecontact is first inserted into the collet sleeve 27 through the end ofbore 13 which opens to the block rear wall 12. The contact 20 is thenurged further into the collet 26 until the contact head 22 engages andspreads the fingers 32-35 and a radial back wall E0 of the contact head22 moves past the radial walls 49 of the finger head portions 40. Thefingers then snap radially inwardly to the positions thereof shown inFIGURE 1 wherein the radial back wall 50 of the contact head 22 providesa shoulder surface in abutting engagement with the shoulder surfaces 49of the fingers 32-35.

When the contact 20 is mounted in assembled relation in the collect 26the inner peripheral wall portions 48a of each of the nger head portions40 are in engaging relation with the adjacent surfaces ofthe contactshank 21. Similarly, the inner Peripheral wall portions 48h of each ofthe finger head portions 40 are in engaging relation with the adjacentsurfaces of the contact head 22.

As noted hereinabove, a principal object of the present invention is toprovide a collet having a contact removal capability flar in excess ofthe contact removal capability of the collets or contact mountingmembers of the prior art. Failure of the fingers (or tines) of the priorart collets results, generally, during flexure of the collet fingers inorder to release the contacts from the collet and allow its removal fromthe connector.

In most instances, the forces required to fiex the fingers createstresses in the beam portion of the fingers which closely approach theyield strength of the material of which the fingers `are made. It iswell known that all metals are crystalline, and that repeated stresswill result in the mechanism of fatigue failure which occurs when theendurance limit of the material is exceeded. This phenomenon occursduring repeated stress, even though under static conditions, the normalstress may be well within the yield streng'h of the material.

The collet 26, however, constructed in accordance with the principles ofthis invention, is capable of withstanding a vastly increased number ofcontact removal and reinsertion operations. The collet 26 is machined sothat the thicknesses of portions thereof differ from one another and theentire configuration of the collet and the contours and dimensions ofits various portions are carefully selected and controlled. This is incontrast with the fabrication methods of the prior art wherein thecollets are generally merely stamped from sheets of fiat stock, ormachined, wth regard only to the static stresses of the colletstructure.

The collet 26 may be rnade of beryllium copper which affords goodresilient fiexibility to the fingers 32-35. As noted, the fingers 32-35impose a radial inward bias on the contact 20 in the assembled statethereof.

A graphic illustration of this force as well as the other forces whichmay be imposed on the fingers 32-35 are shown in the force diagrams ofFIGURES 5, 6 and 7, wherein reference numerals similar to those shown inFIGURES 1-4 Kare used where applicable to indicate similar portions ofthe collet 26.

Assume that a male contact 20 is seated in a collet 26 and that an axialforce indicated at F is being imposed on the shoulder 49 of the headportion 4t). This force may result from mating of the male contact 20with a complemental female contact, or from any undesirable encounterwith another body. An equal and opposite force F is imposed on the wall55 of the fillet 46. As a result of the axially offset relation of theseforces and of the included angle between the beam portion 39 and theaxis of the contact 20, equal and opposite radial forces C and C areimposed respectively on the shoulder 49 and the wall 55. A compressiveforce F is imposed on the beam portion 39. Forces C and C' may becalculated through the equation where D and L represent respectively thedistances with which F and F and C and C are offset with respect to oneanother, reference being made to FIGURE 7.

The force C is augmented by a similarly directed force P caused by thedeflection of the finger 32 from its free state to its assembled statedisposition which occurs when the contact 20 is inserted into the collet26. Forces T and T result from imperfections in the petpendicularity ofcontract radial wall t) and collet radial wall 49 related to the axialcenter line of Contact 2t) and collet 26. These imperfections may resultin an out of perpendicularity as great as Vxhen force F is imposed, asnoted previously, a force T, proportional to F in the ratio of thetangent of 15, tends to radially displace the collet linger 32, inopposition to forces C-l-P and Cl-P.

In accordance with the principles of the present invention the fingers32-35 are constructed so that with respect to each the force P|C whichtends to urge the finger against the contact 2li is always at leasttwice as great as is force T which tends to spread the linger.

It has been determined that optimum results lare obtained when thedistance L is within a range of between 4 to 9 times the distance D.Further, the median diameter of the shoulder 49 in the assembled statethereof should be at least 1.1 times the median diameter thereof in thefree state. The median diameter of the abutment wall 5S should be atleast 1.3 times the median diameter of the shoulder 49 in the assembledstate of the collet. The beam portion 39 should extend at an angle tothe axis of the sleeve 27 in a range of between 5-10 in the free statethereof and in a range of between 3-5 in the assembled state thereof.

The iillet 46 between the major and beam portions 38 and 39 not onlyincreases the radially inward bias of the finger 32 as the lingersspread from its free state to its assembled state configuration, butalso greatly improves the stress distribution at this highly criticaljunction.

The bending moment and stress distribution of linger 32 (as well asngers 33-35) are shown graphically in FIGURE L8. The bending momentshown in the graph is that which occurs along the length of the linger32 after it has been spread from its free state to a deflected positionwhich will allow the contact 2t) to be removed from collet 26. Thedeflection in this example is .013. The Stress is that which occursalong the length of the spread finger under the influence of the bendingmoment.

It is noted that while the stress increases at the junction of the majorand beam portions 38 and 39, this increase or concentration of stress islimited to about 1.2 times the normal stress. In the collets of theprior art stress concentrations occur far beyond this 1.2 limitation andare often causes of the relative low contact removal capabilities of theprior art collets.

Referring again to FIGURES 1-4, the fillet 46 comprises, in addition tothe radial end wall 55, an outer peripheral wall 51 which extendssubstantially parallel to the major portion 38, and a transition wall 52which interconnects the peripheral wall 51 and the outer peripheral wall44 of the beam portion 39. The transition wall 52 is inclined toward theaxis `of the collet 26 at an angle greater than the angle of inclinationof the beam portion 39 and comprises an arcuately shape-d section 53adjacent the outer wall 44 of the beam portion 39.

The tillet 46a comprises a radially outwardly inclined transition Wall54 which interconnects the outer Walls 44 and 47 of the beam and headportions 39 and 40, respectively. The transition wall 54 includes anarcuately shaped section 56 immediately adjacent the outer wall 44 ofthe beam portion 39.

As noted, the sleeve 27 is circumferentially continuous. Each of thefingers 32-35 comprises apair of longitudinal end walls 57 and 5S whichextend in circumferentially spaced parallel relation to thelongtiu-dinal end walls 57 and 58 of adjacent fingers. The facinglongitudinal end walls 57 and 58 of adjacent lingers are interconnectedby an arcuately shaped wall 59.

When the collet 26 is inserted into the bore 13 of the insulator block;10, the head portions 40 olt the fingers 32-35 are squeezed togethersufficiently to enable the head portions to pass through the ridge 16projecting inwardly from the bore wall 14. The collet 26 is then pushedforwardly from the back wall 12 of the block 10 into the bore 13 and asthe transition walls 52 of the fingers 32-35 abut the end wall 19 of theridge 16, the fingers 32-35 are wedged together to enable the fillets 46to move past the inner wall 17 of the ridge 16. As soon as the radialend walls 55 of the fillets 46 have passed axially forwardly of the endwall 18 of the ridge 16, the lingers 32-35 snap radially outwardly andthe collet 26 is snaplocked in the bore 13. Once the collet 26 is lockedin the bore 13 it is ready to receive one of the contact members 20'.

Portion 48C of the inner wall 48 of each of the head portions 40 istapered to receive a complementary tapered nose of a tubularly shapedcontact removal tool. As it will be understood by those skilled in theart, the tool may be inserted into the bore 13 from the front side 11 ofthe block 10 to spread the fingers 32-35, whereupon the contact 20 canbe removed from the back side 12 of the block 10. The diameter of thebore wall 14 is sutiicient to enable the fingers 32-35 to be spreadradially outwardly an amount necessary to move the wall 49 out of axialregistry with the wall 50 of the Contact 20.

Another embodiment of a collet constructed in accordance with theprinciples of this invention is shown in FIGURES 9-11 wherein partssimilar to those shown in FIGURES 1-4 are identified by the referencenumerals used in FIGURES 1-4 with the prefix l added.

Thus the collet 126 is mounted in a bore 113 of a connector insulatorblock 11i). The collet 126 has four fingers 132-135 projecting from acircumferentially continuous sleeve 127. A major difference between thisembodiment, however, and the embodiment of FIGURES 1-4 resides in thearrangement for mounting the collet within the u bore.

The major portion 138 of each of the fingers 132-135 comprises an outerperipheral wall 142 and a radial wall to receive the walls 117 and 118of the ridge 116, but the back wall 119 of the ridge 116 abuts a radialwall 16) of a radially outwardly projecting protuberance 161 formed onthe major portion 138, rather than the front wall 30 of the sleeve 27 asshown in the other embodiment.

The protuberance 161 also comprises .a peripheral wall 162 ofsubstantially the same diameter as the wall 151 of the tillet 146, andanother radial wall 163 spaced axially rearwardly of wall but axiallyforwardly of the forward wall 130 of the sleeve 127.

In this arrangement the groove which receives the ridge 116 (and whichis bounded by walls 117, 155 and 163) is spaced further forwardly of thecircumferentially continuous sleeve 127 than in the embodiment ofFIGURES 1-4.

As a result the fingers 132-135 are more easily urged into the bore 113since the wedging surfaces or transition walls 52 are farther from thepoint at which the lingers 132-135 pivot about the sleeve 127.

An end portion 164 of the sleeve 127 is ared outwardly to facilitateinsertion of the head 122 of the contact 120` into the collet 126. Inother respects the collet 126 is similar to collect 26 of FIGURES 1-4.

Although minor .modifications might be suggested by those versed in theart, it should be understood that I wish to embody within the scope ofthe patent warranted hereon all such modifications as reasonably comewithin the scope of my contribution to the art.

I claim as my invention:

1. A tubular machined collet for insertion into a rigid bore of anelectrical connector for receiving and securing therewithin anelectrical contact comprising,

a cylindrical sleeve portion,

a plurality of resilient contact-securing lingers projecting generallyaxially in one direction from said sleeve portion and bendable radiallyoutwardly from a free state configuration to a bore-insertedcontact-sccuring conguration,

said fingers each comprising, in lprogressively axially spaced relationwith respect to said sleeve portion,

a ,major portion, a beam portion and a head portion having first, secondand third inner and outer Aperipheral wall means, respe-ctively,

said first and second inner peripheral wall means having adjacent endsjoining one another, the adjoining end of said first inner peripheralwall means extending axially and the adjoining end of said second innerperipheral wall means sloping radially inwardly in said one directionfrom said first inner peripheral wall means,

said second outer peripheral wall means sloping radially inwardly inboth the free state and the bore-inserted contact-securing configurationof said finger in parallel relation to said second inner peripheral wallmeans, and

'a projection forming an abutment wall extending radially outwardly ofsaid first outer peripheral wall means in axially spaced relation tosaid sleeve portion for providing with said sleeve portion and saidfirst outer peripheral wall means in the outer periphery of said colletcircumferential groove means for receiving a complementarily shapedridge in the bore `of the connector for locking the collet axially inboth directions in the bore,

said third inner peripheral wall means providing a substantiallyradially extending shoulder surface on said head portion facing theprojecting end of said finger for receiving in abutting engagement acooperating shoulder formed on a head of the electrical contact and acontact-head surrounding surface extending axially from said shouldersurface for surrounding the head of the electrical contact.

2. The collet as defined in claim 1 wherein said projection comprises afillet including a radially inwardly and axially extending transitionwall interconnecting said first and second outer peripheral wall meansand including an arcuately shaped concave section immediately adjacentsaid second outer peripheral wall means to enhance stress distributionand to increase fatigue resistance and durability of the collet in thearea of the junction of the major beam portions of said fingers.

3. The collet as defined in claim 1 and including a radially outwardlyland axially extending transition wall interconnecting said second andsaid third o-uter peripheral wall means,

said transition wall being concave throughout a substantial portion ofthe axial extent thereof to enhance stress distribution and to increasefatigue resistance and durability of the collet in the area of thejunction of the beam and head portions of said fingers.

4. The collet as defined in claim 2 wherein the thickness of said filletin a radial plane is in the range of between 1.2 and 2.3 times thethickness of said beam portion in a radial plane.

5. In a collet for retaining an electrical contact in a connector, madeof machinable material, the improvement of inner and outer surfaces ofrevolution forming together with one another and characterized by,

a first shoulder projecting in one radially transverse ydirection fromone of said surfaces,

a second shoulder spaced axially from said first shoulder and projectingin an opposite radially transverse direction from the other of saidsurfaces,

an interconnecting beam section extending axially and radially betweensaid shoulders,

said first and second shoulders being radially spaced at an unstressedposition `so that axial forces applied thereto will develop lacountermoment counteracting bending moments tending to render said beamsection unstable, and transition portions connecting said first andsecond shoulders at corresponding inner and outer surfaces to said beamsection without significant discontinuities,

said inner and outer surfaces at said beam section 'and at saidtransition portions comprising means disposed in such configurativerelationship with respect to one another that the stresses in such beamsection and said transition portions will be so smoothly distributedthat stress concentrations will be limited to no more than 1.2 times thenormal stress.

6. The collet as defined in claim 5 wherein said shoulders are subjectedto oppositely acting and axial forces and wherein the vaxial distancebetween said shoulders is within a range of between 4 to 9 times theradial distance between the lines of said forces acting on saidshoulders.

7. The collet as defined in claim 5 wherein said second shoulder isimovable radialy outwardly from a free state position to acontact-inserted position and wherein the median diameter of said secondshoulder in the contact-inserted position thereof is at least 1.1 timesthe median diameter thereof in said free state position.

8. The collet as defined in claim 5 wherein said second shoulder ismovable radially outwardly from a free state position to acontact-inserted position and wherein the median diameter of said firstshoulder is at least 1.3 times the diameter of said second shoulder insaid contact-inserted position thereof.

9. The collet as defined in claim 5 wherein said beam section isbendable radially outwardly from a free state configuration to acontact-inserted configuration and wherein said beam section extends atan angle to the axis of said collet in a range of between 5-10 in thefree state configuration thereof and in a range of between 3-5 in thecontact-inserted configuration thereof.

10. The collet as defined in claim 5 wherein said transition portionscomprise concavely-shaped wall surfaces enhancing the distribution ofstress at the areas of juncture of said shoulders and said beam section.

11. A tubular machined collet for insertion into a rigid bore of anelectrical connector for receiving and securing therewithin anelectrical contact comprising,

a cylindrical sleeve portion,

a plurality of resilient contact-securing fingers projecting generallyaxially in one direction from said sleeve portion and bendable radiallyoutwardly from `a free state configuration to a bore-insertedcontact-securing configuration,

sa1d fingers each compr1s1ng, 1n progressively ax1ally spaced relationwith respect to said sleeve portion, a major portion, a beam portion anda head portion having first, second and third inner and outer peripheralwalls, respectively,

said first and second inner peripheral Walls having adjacent endsjoining one another, the iadjoining end of said first inner peripheralwall extending axially and the 'adjoining end of said second innerperipheral wall sloping radially inwardly in said one direction fromsaid first inner peripheral wall,

said second outer peripheral wall also sloping radially inwardly in boththe free state and the bore-inserted contact-securing configuration ofsaid linger, and

a projection forming an abutment wall extending radially outwardly ofsaid first outer peripheral wall in axially spaced relation to saidsleeve portion for providing with said sleeve portion and said firstouter peripheral wall in the outer periphery of said colletcircumferential groove means for receiving a complementarily shapedridge in the bore of the connec- 1 l 1 2 tor for locking the colletaxially in both directions stress concentrations therein when assembledin the in the bore, connector and when securing a contact therewithinsaid third inner peripheral Wall `providing a subby smoothlydistributing stress to maintain concenstantially radially extendingshoulder surface on trations at all points along the axial extentthereof said head portion facing the projecting end of 5 no greater than1.2 times the normal stress.

said finger for receiving in abutting engagement a cooperating shoulderformed on a head of the References Clted electrical contact and acontact-head surround- UNITED STATES PATENTS ing surface extendingaxially from said shoulder 2,477,849 8/ 1949 Adams 339-217 surface forsurrounding the head of the eleclo 3,221,292 11/1965 Swanson et a]339-217 trical Contact, 3,229,244 1/1966 Bachman 339-217 said abutmentWall and said shoulder surface be- 3,246,281 4/ 1966 Cunningham 339-217ing spaced axially and radially from one another and being subjected tooppositely directed axial FOREIGN PATENTS forces, 15 936,926 9/ 1963Great Britain. said projection further comprising an axially extendingtransition Wall sloping radially inward- MARVIN A- CHAMPION, PrimaryExaminer- 1y t0 Said Sfod Outer Peripheral Wall, R. s. sTRoBEL,Assistant Examiner. said lingers compr1sing means configured to minimize

